Good request. If you are writing a paper on this, then the first thing you need to do is ask whether you agree. If you do not agree, then you need to state this and offer some reason why you think this way.
If you agree, then you need to show why leaders are important. I happen to think that leaders are very important. Here are my reasons:
(1) Leaders usually have a mission statement and they set the tone. If the mission is poor, then so will the organization.
(2) Leaders provide the feel of the culture. If the leader is nurturing, yet firm, then the organization may thrive.
(3) Finally, leaders troubleshoot when things go awry and they always will. To build consensus during this time is absolutely key.
In answering this question, I believe that you can go in many directions. Much of this is dependent on what research and study you have in your direct grasp and your own belief system. I would propose that to start this, ask yourself why is leadership important. Think of any situation where leadership in a complex problem must be asserted. What is gained from this leadership component? Answering this can have relevancy in any organizational capacity. Last evening, President Obama exhibited a great deal of leadership in articulating his vision for United States involvement in Afghanistan. This could serve as an excellent starting point for an introduction to the topic. When you have examined why leadership is needed, I think you will have to address the various models of leadership and how specific targets can be met through the employment of different models of leadership. In articulating the need and execution of leadership, I think you will go very far in proving how vital it is to the successful execution of any organization.